U.S. patent number 4,126,406 [Application Number 05/722,768] was granted by the patent office on 1978-11-21 for cooling of downhole electric pump motors.
This patent grant is currently assigned to TRW Inc.. Invention is credited to Bert Benear, Francis T. Traylor, Frank J. Vatalaro.
United States Patent |
4,126,406 |
Traylor , et al. |
November 21, 1978 |
Cooling of downhole electric pump motors
Abstract
Efficient downhole cooling of the electric pump motor, motor
protector, and thrust bearing of a submergible pump assembly in a
high temperature environment is accomplished without significant
modification of the pump assembly itself. Coolant flows through an
insulated shroud as a high velocity annular fluid sheet surrounding
the components to be cooled. In a closed loop system, coolant from
a heat exchanger is supplied to the shroud via insulated supply
tubing, which contains a cable for energizing the motor, is
injected into the shroud by a coolant discharge head from which the
pump assembly is suspended, and returns to the heat exchanger via
insulated return tubing. The walls of the shroud and tubing include
expansion element which accommodate the difference between interior
and exterior temperatures.
Inventors: |
Traylor; Francis T.
(Bartlesville, OK), Vatalaro; Frank J. (Bartlesville,
OK), Benear; Bert (Bartlesville, OK) |
Assignee: |
TRW Inc. (Cleveland,
OH)
|
Family
ID: |
24903301 |
Appl.
No.: |
05/722,768 |
Filed: |
September 13, 1976 |
Current U.S.
Class: |
417/373; 310/64;
310/87; 417/367 |
Current CPC
Class: |
E21B
36/003 (20130101); F04D 13/10 (20130101); F04D
29/586 (20130101); H02K 5/132 (20130101); H02K
9/19 (20130101) |
Current International
Class: |
E21B
36/00 (20060101); F04D 13/06 (20060101); F04D
13/10 (20060101); F04D 29/58 (20060101); H02K
5/12 (20060101); H02K 5/132 (20060101); H02K
9/19 (20060101); F04B 039/06 () |
Field of
Search: |
;417/366,367,373
;310/53,58,64,87 ;415/521 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Croyle; Carlton R.
Assistant Examiner: Gluck; R. E.
Attorney, Agent or Firm: Shapiro and Shapiro
Claims
The invention claimed is:
1. In combination with a submergible pump assembly having means for
suspending the pump assembly downhole in a well and including an
electric pump motor, a motor protector, and a pump at the bottom of
the assembly, cooling apparatus for the motor and motor protector
and comprising a tubular shroud surrounding the exterior surface of
the motor and the motor protector at the downhole location of the
pump assembly and providing interiorly of the shroud and exteriorly
of the motor and the protector a chamber above said pump isolated
from the exterior of the shroud, said chamber having an insulated
side wall, a coolant discharge head at one end and a coolant
exhaust port at the other end, and insulated conduit means
extending downhole in the well to the shroud for circulating
coolant through said chamber via said discharge head and said
exhaust port, the coolant discharge head being located in a
downhole location at the top of said shroud and having means for
distributing coolant around the interior of the shroud, and said
pump assembly being suspended from said coolant discharge head.
2. The combination of claim 1, wherein said conduit means comprises
coolant supply tubing suspending said coolant discharge head
therefrom and containing an electrical cable for energizing said
motor, and wherein said coolant discharge head includes a chamber
for the splicing of conductors of said cable to lead-in conductors
of said motor.
3. The combination of claim 2, wherein the side wall of said shroud
and the walls of said conduit means include expansion members for
accommodating thermal expansion.
4. The combination of claim 1, wherein a section of coolant flow
tubing extends from said port to said one end of said shroud
exteriorly of said shroud and wherein said conduit means comprises
a supply conduit coupled to said discharge head and a return
conduit connected to said section of tubing.
5. The combination of claim 1, wherein said insulated side wall
comprises inner and outer walls separated by insulation.
6. The combination of claim 5, wherein said shroud has means for
permitting thermal expansion of one of said inner and outer walls
relative to the other.
7. The combination of claim 1, wherein said conduit means is
connected in a closed loop cooling system including a heat
exchanger.
8. The combination of claim 7, wherein said conduit means comprises
insulated tubing connecting said shroud to said heat exchanger.
9. The combination of claim 8, wherein said insulated tubing
comprises inner and outer walls separated by insulation and has
expansion means for permitting thermal expansion of one of said
walls relative to the other.
10. The combination of claim 1, wherein the major exterior surfaces
of the motor and the protector are closely spaced from the inner
surface of the insulated shroud side wall to provide a thin annular
high velocity coolant flow passage, the thickness of said passage
being orders of magnitude less than the diameter of the motor and
the protector.
11. The combination of claim 1, wherein the pump has an intake at
its bottom and a discharge head at its top located at separated
portions of the well.
Description
BACKGROUND OF THE INVENTION
This invention is concerned with cooling downhole electric pump
motors and associated apparatus in high temperature
environments.
It has been conventional practice to employ ambient-temperature
well fluid as a medium for dissipating the heat generated by the
electric motors of submergible pumps. In wells with ambient
downhole temperatures of up to about 250.degree. F., this technique
has been satisfactory. With substantially higher downhole
temperatures, e.g. 300.degree. F.-500.degree. F., as may be
encountered in geothermal wells, the well fluid is too hot to serve
as the required heat dissipation medium, and the insulation,
lubricant, and bearing materials of commercially available pump
assemblies suffer from the effects of high temperature. It has, of
course, been known to circulate coolants through electric motors,
but such techniques have certain complexities, including, usually,
the need for specialized motor or heat exchanger structures.
BRIEF DESCRIPTION OF THE INVENTION
It is a principal object of the present invention to provide
adequate cooling of downhole electric motors and associated
apparatus in high temperature environments without significant
modification of commercially available submergible pump
assemblies.
Briefly stated, but without intent to limit the scope of the
invention, a preferred embodiment of the invention employs a shroud
having an insulated tubular wall providing a chamber enveloping the
downhole electric motor, motor protector and thrust bearing of a
submergible pump assembly. A coolant, preferably water, is
circulated through the shroud via insulated coolant supply and
return tubing, the former being coupled to the interior of the
shroud by a coolant discharge head and the latter being coupled to
the interior of the shroud by an exhaust port. The coolant flows
through the shroud as a high velocity annular sheet surrounding the
cooled apparatus and is then returned to a heat exchanger at the
earth's surface, from which the coolant is pumped into the supply
tubing. The pump assembly is suspended from the supply tubing by
the coolant discharge head. An electric cable for energizing the
pump motor is contained in the supply tubing and is spliced to
lead-in conductors of the motor in a chamber of the coolant
discharge head. Thermal expansion effects are accommodated by
expansion elements associated with the walls of the tubing and the
shroud.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further described in conjunction with the
accompanying drawings, which illustrate a preferred and exemplary
embodiment, wherein:
FIG. 1 is a diagrammatic longitudinal sectional view illustrating
apparatus of the invention in a well;
FIG. 2 is a further view of the apparatus of FIG. 1 shown enlarged
and broken into sections for convenience of illustration;
FIG. 3 is a contracted longitudinal sectional view of the shroud,
coolant discharge head and return tubing; and
FIG. 4 is a fragmentary longitudinal sectional view of a portion of
the tubing including an expansion member.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, and initially to FIGS. 1 and 2, the
invention is shown, for purposes of illustration, in its
application to a geothermal well having a well casing 10 in which a
submergible pump assembly 12 is located downhole. The pump assembly
comprises a submergible pump 14, which may be of the well-known
centrifugal type, for example, and a pump motor and motor protector
described hereinafter. A conventional packer 16 separates a first
portion of the well, at which an intake nipple 18 of the pump is
located, from a second, higher pressure portion at which the well
fluid discharge head 20 of the pump is located.
Pump 14 is driven by an electric motor 22, which is connected by an
electrical cable 24 to an electrical power source at the earth's
surface. The motor may be a well-known oil-filled type, for
example. A conventional motor protector 26, which may be of the
type shown in U.S. Pat. No. 2,783,400, for example, is shown
interposed between the motor 22 and the pump 14 and contains a
thrust bearing (not shown) which may be of the type shown in the
aforesaid U.S. patent, for example. Submergible pumps, electric
pump motors, and motor protectors suitable for use in the invention
are manufactured and sold by Reda Pump division of TRW, Inc., the
assignee of the present invention. Details of such apparatus may be
found in the following U.S. Pat. Nos., in addition to that noted
above, all of which are assigned to the same assignee and are
incorporated herein by reference: 2,236,887; 2,251,816; 2,270,666;
2,283,118; 2,315,917; 3,433,986; and 3,468,258. Other types of
submergible pump assemblies may also be utilized in the
invention.
In the form shown, the pump assembly is suspended from a wellhead
28 at the earth's surface by means of suspension tubing 30. The
wellhead includes a well fluid discharge pipe 32 and the usual
flanges 34 and 36. It will be noted that in the preferred
embodiment of the invention the pump is at the bottom of the pump
assembly, i.e., below the motor, rather than above the motor as is
frequently the arrangement in submergible pump assemblies. The
preferred arrangement, with the motor at the top of the pump
assembly, is significant in reducing the complexity required for
adequate cooling, as will become apparent hereinafter.
In accordance with the preferred embodiment of the invention, motor
22, motor protector 26 and the thrust bearing therein, are
surrounded by a shroud 38. As shown in FIG. 3, shroud 38 has an
insulated tubular side wall comprising coaxial inner and outer
walls 40 and 42 (e.g., 6 inch O.D. .times. 5.625 inch I.D. and 7
inch O.D. .times. 6.500 inch I.D. steel tubing, respectively)
separated by insulation 44, which may be of Foamglas, for example.
The side wall extends between and is connected to upper and lower
annular end pieces 46 and 48, as by welding. The space between
inner and outer walls 40 and 42 is sealed by appropriate sealing
means to maintain the insulation dry and may also be pressurized.
An annular slot 50 in end piece 46 accommodates thermal expansion
of outer wall 42 with respect to inner wall 40. End pieces 46 and
48 have recesses 52 and 54 into which opposite ends of a section of
coolant return tubing 56 are received and sealed. The coolant
return tubing is also insulated, comprising coaxial inner and outer
walls 58 and 60 (which may be of steel tubing) separated by
insulation 62, which may be of the same type as that employed in
the shroud. Again the insulation is sealed from ambient to maintain
it dry. A threaded receptacle 64 in the upper end piece 46 receives
the threaded lower end of a further section 66 of similarly
constructed coolant return tubing as shown in FIGS. 1 and 2. The
lower end of section 56 communicates with the interior of the
shroud through a coolant exhaust port 68, which may be drilled
radially into end piece 48 and blocked externally by a plug 70.
As shown in FIG. 2, in the illustrative form of the invention the
suspension tubing 30 for the pump assembly is employed as the
coolant supply tubing. Tubing 30 is also coaxial, comprising inner
and outer walls 72 and 74 separated by insulation 76. The
construction of the supply tubing 30 may be similar to the return
tubing, but in the form shown the central passage within wall 72 is
large enough to accommodate electrical cable 24 and yet provide a
space surrounding the cable for the flow of coolant. Other tubing
arrangements may be employed but the tubing, like the shroud, must
be insulated to prevent heat exchange between the coolant and the
well fluid. In a closed loop system, the coolant, preferably water,
is delivered from a heat exchanger at the earth's surface by a
coolant pump, as indicated diagrammatically by block 78. Suitable
pressure and temperature gauges 80 and 82 may be provided in the
supply line 84 delivering the coolant to a coolant injection tee 86
at the top of suspension tubing 30. Cable 24 enters the suspension
tubing through a conventional cable seal 88. The coolant return
line 90 may also be provided with pressure and temperature gauges
92 and 94. While it is apparent that in the preferred form of the
invention a closed loop coolant circulating system is employed,
isolating the coolant from the well fluid and avoiding the need for
supplying large quantities of coolant, in theory the coolant could
be discharged after one pass through the shroud.
Shroud 38 is supported upon pump assembly 12 by conventional means,
such as rings 96 and 98 threaded onto or otherwise attached to
shroud-supporting components at opposite ends of the shroud. In the
illustrative embodiment ring 98 is attached to the lower end of
protector 26 (which is sealed into lower end piece 48 by
conventional seals), while ring 96 is attached to a coolant
discharge head and cable connecting chamber 100. As shown in FIG.
3, this member is a sleeve, which may be internally threaded at the
top for receiving external threads at the lower end of suspension
tubing 30 and which may be externally threaded at the bottom for
engagement with the internal threads of an adaptor 102 (FIF. 2) by
which the pump assembly is suspended from the coolant discharge
head 100. Plural coolant distributing passages 104, spaced
circumferentially of the coolant discharge head for uniform
distribution of coolant, extend longitudinally from a chamber 106
beneath the lower end of the suspension tubing and terminate in
transverse bore portions 108 leading radially to the exterior of
the coolant discharge head, which is spaced from shroud wall 40 for
discharging coolant into the shroud 38. The major exterior surfaces
of the motor and the protector are spaced slightly from the
interior surface of the shroud side wall to provide a thin annular
flow passage, the thickness of which is orders of magnitude less
than the diameter of the components to be cooled. Lead-in
conductors for energizing motor 22 extend through a central bore
110 and are spliced to the lower end of the conductors of cable 24.
A conventional cable seal (not shown) is provided to prevent the
coolant from entering bore 110. A typical lead-in arrangement is
shown in U.S. Pat. No. 2,283,117, assigned to the assignee of the
present invention and incorporated herein by reference. O-rings 112
seal the coolant discharge head into the upper end piece 46 of the
shroud. The interior of the shroud is thus isolated from the well
fluid. To maintain tubing insulation isolated both from the well
fluid and the coolant, an expansion member 114, such as a bellows,
is employed in each length of tubing, as shown in FIG. 4 to permit
relative movement of the inner and outer walls to accommodate the
difference between exterior and interior temperatures. Conventional
seals may be employed between successive lengths of tubing.
By virtue of the invention, effective cooling of downhole electric
motors and associated apparatus in high temperature environments is
accomplished without substantial modification of commercially
available pump assembly components. The arrangement of the shroud,
coolant discharge head, and pump assembly, with the pump at the
bottom, permits simple suspension of the pump assembly and
energization of the pump motor while providing the desired cooling.
The provision of a thin annular flow space between the shroud wall
and the cooled apparatus insures sufficient flow velocity for
adequate heat dissipation, without internal modification of the
cooled components, and the thermally insulated shroud wall and
coolant conduit prevent undesirable heat exchange between coolant
and well fluid, providing practical cooling without requiring large
quantities of expensive coolant. Although the invention has been
described in its principal intended application to cooling of
downhole electric motors and associated apparatus, modifications
within the scope of the invention will be apparent to those skilled
in the art. For example, under appropriate conditions, heat might
be supplied rather than removed.
* * * * *